fix: upgrade to latest versions

[vmx]

The latest versions of the gpu dependencies contain support for CUDA. Therefore
the gpu feature is split into cuda and opencl. By default only opencl is
enabled.

BREAKING CHANGE: The gpu feature is replaced by the opencl feature.

[dignifiedquire]

can you update the circle ci config to test both features please?

[vmx]

I thought I concentrate on OpenCL first as this is what we want to ship. Next step would then be CUDA with proper testing, updates of the README etc. So I would make the CUDA stuff a separate PR. Though perhaps it just works, so let's try it out.

[vmx]

I've added a new test run for the test_gpu_tree_building as it's the only test that runs on the GPU. It now runs on OpenCL and on CUDA.

[vmx]

@cryptonemo I leave the merge to you (I couldn't merge anyway due to "Required statuses must pass before merging").

[cryptonemo]

I also don't recall where the required CI tests are checked/unchecked. I'm ok merging this, but want to be sure that CI will not be broken on master from this point forward. Any insight?

[cryptonemo]

Oh wait, I think I found it: https://github.com/filecoin-project/rust-fil-proofs/settings/branch_protection_rules/2848255

If this seem correct (where I can uncheck ones after merging), I'll proceed. Sanity check?

[dignifiedquire]

the required tests changed with the blst/pairing change from the earlier PR

[cryptonemo]

the required tests changed with the blst/pairing change from the earlier PR

I see, I've removed all of the old ones then.